Sonia Cohen

Brain-Specific Phosphorylation of MeCP2 Regulates Activity-Dependent Bdnf Transcription, Dendritic Growth, and Spine Maturation

Mutations or duplications in MECP2 cause Rett and Rett-like syndromes, neurodevelopmental disorders characterized by mental retardation, motor dysfunction, and autistic behaviors. MeCP2 is expressed in many mammalian tissues and functions as a global repressor of transcription; however, the molecular mechanisms by which MeCP2 dysfunction leads to the neural-specific phenotypes of RTT remain poorly understood. Here, we show that neuronal activity and subsequent calcium influx trigger the de novo phosphorylation of MeCP2 at serine 421 (S421) by a CaMKII-dependent mechanism. MeCP2 S421 phosphorylation is induced selectively in the brain in response to physiological stimuli. Significantly, we find that S421 phosphorylation controls the ability of MeCP2 to regulate dendritic patterning, spine morphogenesis, and the activity-dependent induction of Bdnf transcription. These findings suggest that, by triggering MeCP2 phosphorylation, neuronal activity regulates a program of gene expression that mediates nervous system maturation and that disruption of this process in individuals with mutations in MeCP2 may underlie the neural-specific pathology of RTT.

Communication Between the Synapse and the Nucleus in Neuronal Development, Plasticity, and Disease

Sensory experience is critical for the proper development and plasticity of the brain throughout life. Successful adaptation to the environment is necessary for the survival of an organism, and this process requires the translation of specific sensory stimuli into changes in the structure and function of relevant neural circuits. Sensory-evoked activity drives synaptic input onto neurons within these behavioral circuits, initiating membrane depolarization and calcium influx into the cytoplasm. Calcium signaling triggers the molecular mechanisms underlying neuronal adaptation, including the activity-dependent transcriptional programs that drive the synthesis of the effector molecules required for long-term changes in neuronal function. Insight into the signaling pathways between the synapse and the nucleus that translate specific stimuli into altered patterns of connectivity within a circuit provides clues as to how activity-dependent programs of gene expression are coordinated and how disruptions in this process may contribute to disorders of cognitive function.

Loss of Inhibitory Interneurons in the Dorsal Spinal Cord and Elevated Itch in Bhlhb5 Mutant Mice

Itch is the least well understood of all the somatic senses, and the neural circuits that underlie this sensation are poorly defined. Here we show that the atonal-related transcription factor Bhlhb5 is transiently expressed in the dorsal horn of the developing spinal cord and appears to play a role in the formation and regulation of pruritic (itch) circuits. Mice lacking Bhlhb5 develop self-inflicted skin lesions and show significantly enhanced scratching responses to pruritic agents. Through genetic fate-mapping and conditional ablation, we provide evidence that the pruritic phenotype in Bhlhb5 mutants is due to selective loss of a subset of inhibitory interneurons in the dorsal horn. Our findings suggest that Bhlhb5 is required for the survival of a specific population of inhibitory interneurons that regulate pruritus, and provide evidence that the loss of inhibitory synaptic input results in abnormal itch.

Activity-dependent phosphorylation of MeCP2 threonine 308 regulates interaction with NCoR

Rett syndrome (RTT) is an X-linked human neurodevelopmental disorder with features of autism and severe neurological dysfunction in females. RTT is caused by mutations in methyl-CpG-binding protein 2 (MeCP2), a nuclear protein that, in neurons, regulates transcription, is expressed at high levels similar to that of histones, and binds to methylated cytosines broadly across the genome. By phosphotryptic mapping, we identify three sites (S86, S274 and T308) of activity-dependent MeCP2 phosphorylation. Phosphorylation of these sites is differentially induced by neuronal activity, brain-derived neurotrophic factor, or agents that elevate the intracellular level of 3′,5′-cyclic AMP (cAMP), indicating that MeCP2 may function as an epigenetic regulator of gene expression that integrates diverse signals from the environment. Here we show that the phosphorylation of T308 blocks the interaction of the repressor domain of MeCP2 with the nuclear receptor co-repressor (NCoR) complex and suppresses the ability of MeCP2 to repress transcription. In knock-in mice bearing the common human RTT missense mutation R306C, neuronal activity fails to induce MeCP2 T308 phosphorylation, suggesting that the loss of T308 phosphorylation might contribute to RTT. Consistent with this possibility, the mutation of MeCP2 T308A in mice leads to a decrease in the induction of a subset of activity-regulated genes and to RTT-like symptoms. These findings indicate that the activity-dependent phosphorylation of MeCP2 at T308 regulates the interaction of MeCP2 with the NCoR complex, and that RTT in humans may be due, in part, to the loss of activity-dependent MeCP2 T308 phosphorylation and a disruption of the phosphorylation-regulated interaction of MeCP2 with the NCoR complex.

Rett syndrome mutation MeCP2 T158A disrupts DNA binding, protein stability and ERP responses

Mutations in the MECP2 gene cause the autism spectrum disorder Rett syndrome (RTT). One of the most common MeCP2 mutations associated with RTT occurs at threonine 158, converting it to methionine (T158M) or alanine (T158A). To understand the role of T158 mutations in the pathogenesis of RTT, we generated knockin mice that recapitulate the MeCP2 T158A mutation. We found a causal role for T158A mutation in the development of RTT-like phenotypes, including developmental regression, motor dysfunction, and learning and memory deficits. These phenotypes resemble those present in Mecp2 null mice and manifest through a reduction in MeCP2 binding to methylated DNA and a decrease in MeCP2 protein stability. The age-dependent development of event-related neuronal responses was disrupted by MeCP2 mutation, suggesting that impaired neuronal circuitry underlies the pathogenesis of RTT and that assessment of event-related potentials (ERPs) may serve as a biomarker for RTT and treatment evaluation.

Bhlhb5 and Prdm8 form a repressor complex involved in neuronal circuit assembly

Although transcription factors that repress gene expression play critical roles in nervous system development, their mechanism of action remains to be understood. Here, we report that the Olig-related transcription factor Bhlhb5 (also known as Bhlhe22) forms a repressor complex with the PR/SET domain protein, Prdm8. We find that Bhlhb5 binds to sequence-specific DNA elements and then recruits Prdm8, which mediates the repression of target genes. This interaction is critical for repressor function since mice lacking either Bhlhb5 or Prdm8 have strikingly similar cellular and behavioral phenotypes, including axonal mistargeting by neurons of the dorsal telencephalon and abnormal itch-like behavior. We provide evidence that Cadherin-11 functions as target of the Prdm8/Bhlhb5 repressor complex that must be repressed for proper neural circuit formation to occur. These findings suggest that Prdm8 is an obligate partner of Bhlhb5, forming a repressor complex that directs neural circuit assembly in part through the precise regulation of Cadherin-11.

Medicine. Activating a repressor.

A factor implicated in autism spectrum disorders can both suppress and activate the expression of genes involved in neurodevelopment.

MeCP2 Phosphorylation Limits Psychostimulant-Induced Behavioral and Neuronal Plasticity

The methyl-DNA binding protein MeCP2 is emerging as an important regulator of drug reinforcement processes. Psychostimulants induce phosphorylation of MeCP2 at Ser421; however, the functional significance of this posttranslational modification for addictive-like behaviors was unknown. Here we show that MeCP2 Ser421Ala knock-in mice display both a reduced threshold for the induction of locomotor sensitization by investigator-administered amphetamine and enhanced behavioral sensitivity to the reinforcing properties of self-administered cocaine. These behavioral differences were accompanied in the knock-in mice by changes in medium spiny neuron intrinsic excitability and nucleus accumbens gene expression typically observed in association with repeated exposure to these drugs. These data show that phosphorylation of MeCP2 at Ser421 functions to limit the circuit plasticities in the nucleus accumbens that underlie addictive-like behaviors.

Phosphorylation of MeCP2 at Ser421 Contributes to Chronic Antidepressant Action

Although tricyclic antidepressants rapidly activate monoaminergic neurotransmission, these drugs must be administered chronically to alleviate symptoms of depression. This observation suggests that molecular mechanisms downstream of monoamine receptor activation, which include the induction of gene transcription, underlie chronic antidepressant-induced changes in behavior. Here we show that methyl-CpG-binding protein 2 (MeCP2) regulates behavioral responses to chronic antidepressant treatment. Imipramine administration induces phosphorylation of MeCP2 at Ser421 (pMeCP2) selectively in the nucleus accumbens and the lateral habenula, two brain regions important for depressive-like behaviors. To test the role of pMeCP2 in depressive-like behaviors, we used male mice that bear a germ-line mutation knocked into the X-linked Mecp2 locus that changes Ser421 to a nonphosphorylatable Ala residue (S421A). MeCP2 S421A knock-in (KI) mice showed increased immobility in forced-swim and tail-suspension tests compared with their wild-type (WT) littermates. However, immobility of both MeCP2 WT and KI mice in forced swim was reduced by acute administration of imipramine, demonstrating that loss of pMeCP2 does not impair acute pharmacological sensitivity to this drug. After chronic social defeat stress, chronic administration of imipramine significantly improved social interaction in the MeCP2 WT mice. In contrast, the MeCP2 KI mice did not respond to chronic imipramine administration. These data suggest novel roles for pMeCP2 in the sensitivity to stressful stimuli and demonstrate that pMeCP2 is required for the effects of chronic imipramine on depressive-like behaviors induced by chronic social defeat stress.

The Role of Surgery for Melanoma in an Era of Effective Systemic Therapy

Purpose of ReviewThe recent discovery of effective systemic treatments for melanoma has dramatically improved the prognosis for patients with advanced disease. As a result, the multidisciplinary management of melanoma has evolved significantly. In the past decades surgery was reserved for symptomatic palliation in patients with metastatic melanoma. Today surgical treatment of patients responding to systemic therapies has become an integral part of disease control.Recent FindingsCurrent efforts are focused on minimizing the morbidity of surgery (laparoscopic inguinal lymph node dissection, selective completion lymphadenectomy) as well as combining surgery with systemic therapy in novel ways (neoadjuvant targeted and/or immunotherapy, isolated limb infusion/perfusion with systemic immunotherapy).SummaryThis review examines the use of surgery for advanced melanoma in the era predating modern systemic therapy as well as potential applications moving forward.